However, the BBC's Imogen Foulkes in Geneva says aid agencies have reacted with dismay and anger to the border closures.

The Red Cross said its shipment of chlorine tablets, vital to combating a cholera epidemic which has affected more than 900,000 people, had been blocked.

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Media captionWatch: The reality of life in Yemen

"If these channels, these lifelines are not kept open it is catastrophic for people who are already in what we have said is the world's worst humanitarian crisis at the moment," said Office for the Co-ordination for Humanitarian Affairs spokesman Jens Laerke.

"So this is an access problem of colossal dimensions right now."

The UN says seven million Yemenis are on the brink of famine.

The country relies on imports for virtually everything civilians need to survive, but now neither food, fuel nor medicine can get in.